Masters Theses

Date of Award

5-2005

Degree Type

Thesis

Degree Name

Master of Science

Major

Engineering Science

Major Professor

Richard D. Komistek

Committee Members

Mohamed R. Mahfouz, William R. Hamel

Abstract

This study deals with the development of a computational method that generates the in-vivo contact pressures on the superior side of the polyethylene in total knee arthroplasty (TKA) based on in-vivo kinematic data. Ten clinically successful subjects (five fixed and five mobile bearing TKA), having Hospital for Special Surgery (HSS) knee scores greater than 90, were analyzed under fluoroscopic surveillance while performing a weight-bearing deep knee bend. 3D in-vivo contact positions and kinematics, determined using a 2D to 3D registration technique, and soft tissue locations derived from literature were entered into a 3D inverse dynamics mathematical model to determine the in-vivo bearing contact forces. The contact areas were obtained by assembling the 3D CAD models of the components and measuring the interference area between them. The contact pressure was calculated by dividing the contact forces with the contact areas. For subjects with the mobile bearing TKA the average lateral contact forces varied from 0.34BW to 0.91BW and the average medial contact forces varied from 0.5BW to 2.7BW from full extension to full flexion. In subjects with the fixed bearing TKA the average contact forces ranged from 0.43BW to 0.92BW and from 1.04BW to 2.73BW on the lateral and medial sides respectively from full extension to full flexion. The contact areas for the mobile bearing TKA was always higher than the fixed bearing TKA. The average medial contact pressures ranged from 5.49MPa to 25.7MPa and from 12.8MPa to 34.38MPa for the mobile and fixed bearing TKA respectively. The average lateral contact pressures varied 3.08MPa to 18.83MPa and from 3.71MPa to 18.36MPa for the mobile and fixed bearing TKA respectively. This study reveals that the in-vivo contact forces and pressures are greater for the medial condyle than the lateral condyle, which is similar to polyethylene retrievals that demonstrate greater posterior-medial wear. Also the ability of the polyethylene insert, in mobile bearing TKA, to rotate helps in maintaining higher femoro-polyethylene contact areas resulting in lesser contact pressures compared to the fixed bearing TKA.

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